a-Si∶H及其多层膜光致发光某些性质的研究

本文研究了 a-Si∶H 及 a-Si∶H/a-SiN_x∶H 多层膜光致发光的某些性质。实验研究表明,a-Si∶H 及其多层膜的光致发光峰值能量强烈地依赖于沉积偏压、a-Si∶H 层厚度和内应力,并对这些结果进行了讨论。     

影响a-Si∶H/a-SiN_x∶H多层膜PPC效应的某些因素

本文由实验给出了曝光强度,多层膜的层数和内应力对 a-Si∶H/a-SiN_x∶H 多层膜持久光电导(PPC)效应的影响及结果分析。     

硼轻掺杂对a-Si∶H光电导层性能影响的研究

用等离子体增强化学气相沉积法制备了厚为1μm左右的B轻掺杂a-Si∶H光电导层，得到了a-Si∶H的暗电导率与淀积工艺参数和B掺杂比关系的实验曲线，利用该曲线确定了最佳工艺参数和最佳掺杂比。测量了最佳参数下淀积的a-Si∶H薄膜的电学和光学性能及其受掺杂比的影响。结果表明，当B掺杂比增大时，a-Si∶H的暗电导率先减小后增大，并可发生几个数量级的变化。光电导率减小，折射率略有降低，线性吸收系数显著增大，光学带隙减小。测量的数据表明，我们制备的B轻掺杂a-Si∶H光电导层满足投影机用液晶光阀的要求。     

SiGe∶H薄膜太阳能电池研究进展

针对氢化非晶硅(a-Si∶H)薄膜太阳能电池在发展过程中所面临的问题,阐述了氢化硅锗(SiGe∶H)薄膜在太阳能电池制备方面的优越性及其最新研究进展,总结了提高SiGe∶H薄膜太阳能电池效率的几种方法,着重介绍了叠层太阳能电池内部运行机理,分析了影响叠层太阳能电池转换效率的因素,最后对SiGe∶H薄膜材料在太阳能电池领域的应用前景以及一些亟待解决的问题进行了展望。     

退火对 a-Si∶H/a-SiN_x∶H 多层膜光致发光和红外吸收谱的影响

本文报道了经300℃到800℃退火后的氢化非晶硅(a-Si∶H)/氢化非晶氮化硅(a-SiN_x∶H)多层膜77K 的光致发光性能。77K 的光致发光峰值能量随 T_a 增加而减少,其减少速度对几种样品是不同的,由厚度为20(?)的 a-Si∶H 子层组成的多层膜(d_(?)=20(?))要来得慢。当退火温度达到800℃时,d_(?)=20(?)的多层膜仍保留有光致发光特性,而对于 d_(?)=300(?)多层膜和单层 a-Si∶H 膜,当退火到600℃后光致发光特性已消失。文中提出了不同 a-Si∶H 子层厚度的多层膜光致发光特性上的差别是与 a-Si∶H/a-SiN_x∶H 界面氢比体内氢热稳定性来得高有关。后者由多层膜的红外吸收谱与退火温度依赖关系得到证实。     

a-Si∶H/a-SiC∶H多层薄膜的光、电特性研究

采用射频等离子体增强化学气相沉积(PECVD)技术,以SiH_4、CH_4和H_2为反应气体,在单晶硅和石英衬底上制备a-Si∶H/a-SiC∶H多层薄膜。利用透射电子显微镜(TEM)对样品的微结构进行了表征,同时对其电子输运性质和光吸收特性进行了实验研究。结果表明,本实验条件下制备的多层薄膜样品为非晶态多层薄膜结构,并且样品具有良好的周期性结构和陡峭的界面特性。室温条件下,样品在垂直方向上呈现出多势垒顺序共振隧穿特性。由于量子限制效应,当a-Si∶H势阱层厚度8nm,随着势阱层厚度减小,样品的光学带隙增大,光吸收系数减小。     

PECVD生长nc-Si∶H膜的沉积机理分析

nc-Si∶H膜具有显著不同于α-Si∶H与μc-Si∶H膜的新颖结构与物性。从热力学反应的基元过程出发，定性地分析了本征nc-Si∶H与掺磷nc-Si(P)∶H膜的沉积机理，并提出了进一步改善膜层质量的新途径     

磷掺杂对a-Si∶H膜晶化特性的影响

本文介绍了不同磷掺杂浓度的 a-Si∶H 膜的结构和电学、光学性质。实验结果表明:轻度的磷掺杂有促进薄膜晶化的作用,从而形成非晶相和微晶相二相混合结构。但当掺磷气体流量比大于5%时,磷掺杂对该膜晶化有抑制作用。这可能是由于在不同掺磷浓度时磷原子在 a-Si∶H 膜中的配位状态不同所致。另外,适当控制工艺条件可以制成高电导(～15Ω~(-1)cm~(-1))和宽带隙(～1.92eV)的优质 n 型 a-Si∶H 膜。     

不同含氮量的a-SiN_x∶H的红外吸收及释氢谱

用红外及氢释放谱研究了由高频辉光放电分解不同配比的 SiH_4+NH_3+H_2混合气体而制备的a-SiN_x∶H 薄膜。结果发现:随着 N/Si 增加,膜的结构由类 a-Si∶H 形式逐渐过渡到类 a-SiN_(1.33)∶H 形式。当 N/Si<0.56,膜的结构以 a-Si∶H 相为主,当 N/Si>0.73时,a-SiN_(1.33)∶H 相起支配作用。在0.56相似文献   

双元素掺杂的a-Si∶H光电特性研究

本文研究由氮(N)、硼(B)以及卤素(X)元素掺杂的 a-Si∶H 膜在静电场下的光电特性.实验结果表明,(B+N)、(B+X)双元素掺杂比单元素更明显地提高 a-Si∶H 膜的表面电位 V_(?),降低残余电位V_R,并在 X/Si=10~(-2),B_2H_6/SiH_4=0.3×10~(-4)时,得到了 V_(?)=60V/μm,σ_D=10~(-4)((?)cm)~(-1)的静电复印用a-Si∶H 材料.     

Detection of change in fluorescence between reactive cyan and the yellow fluorophores using a-SiC:H multilayer transducers

Optical colour sensors based on multilayered a-SiC:H heterostructures can act as voltage controlled optical filters in the visible range. In this article we investigate the application of these structures for Fluorescence Resonance Energy Transfer (FRET) detection, The characteristics of a-SiC:H multilayered structure are studied both theoretically and experimentally in several wavelengths corresponding to different fluorophores. The tunable optical p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures were produced by PECVD and tested for a proper fine tuning in the violet, cyan and yellow wavelengths. The devices were characterized through transmittance and spectral response measurements, under different electrical bias and frequencies. Violet, cyan and yellow signals were applied in simultaneous and results have shown that they can be recovered under suitable applied bias. A theoretical analysis supported by numerical simulation is presented.     

Analysis of single junction a-Si:H solar cells grown on different TCO’s

In consequence of previous investigation of individual transparent conductive oxide (TCO) and absorber layers a study was carried out on hydrogenated amorphous silicon (a-Si:H) solar cells with diluted intrinsic a-Si:H absorber layers deposited on glass substrates covered with different TCO films. The TCO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of using different TCO’s as a front contact in solar cells with structure as follows: Corning glass substrate/TCO (800, 950 nm)/p-type μc-Si:H (∼5 nm)/p-type a-Si:H (10 nm)/a-SiC:H buffer layer (∼5 nm)/intrinsic a-Si:H absorber layer with dilution R = [H₂]/[SiH₄] = 20 (300 nm)/n-type a-Si:H layer (20 nm)/Ag + Al back contact (100 + 200 nm). Diode sputtered ZnO:Ga, textured and non-textured ZnO:Al [3] and commercially fabricated ASAHI (SnO₂:F) U-type TCO’s have been used. The morphology and structure of ZnO films were altered by reactive ion etching (RIE) and post-deposition annealing.It can be concluded that the single junction a-Si:H solar cells with ZnO:Al films achieved comparable parameters as those prepared with commercially fabricated ASAHI U-type TCO’s.     

Maintaining Cu metal integrity on low-k IMDs with a nanometer thick a-SiC:H film obtained by HWCVD

Hydrogenated amorphous silicon carbon (a-SiC:H) ultra thin films obtained by Hot wire chemical vapor deposition (HWCVD) have been shown to act as efficient diffusion barriers for copper on inter metal dielectric (IMD) layers which are of great significance for ultra-large scale integration (ULSI) circuits. In this work, we have studied the influence of the a-SiC:H barrier layer obtained by HWCVD which has implications towards issues related to the resistance to electromigration of Cu in the low dielectric (low-k) hydrogen silsesquioxane (HSQ) film. The presence of the ultra thin a-SiC:H film maintains the integrity of the Cu metal not only by suppressing Cu diffusion but also by increasing its crystallinity, which would have implications with respect to the mean time to failure (MTF) arising from metal electromigration. Though, we demonstrate this aspect on the low-k (HSQ)/Cu system, this should yield similar benefits for other low-k dielectric materials too.     

High rate deposition of a-Si:H and a-SiNx:H by VHF PECVD

Very High Frequency (VHF) plasma enhanced chemical vapour deposition (PECVD) has been applied to hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiN_x:H) films for thin film transistors (TFTs) fabrication. The effect of the excitation frequency on the deposition rate and the film quality of both films has been investigated. The films were prepared by VHF (30 MHz∼50 MHz) and HF (13.56 MHz) plasma enhanced CVD.High deposition rates were achieved in the low pressure region for both a-Si:H and a-SiN_x:H depositions by the use of VHF plasma. The maximum deposition rates were 180 nm/min for a-Si:H at 50 MHz and 340 nm/min for a-SiN_x:H at 40 MHz. For a-SiN_x:H films deposited in VHF plasma, the optical bandgap, the hydrogen content and the [Si–H]/[N–H] ratio remain almost constant regardless of an increase in deposition rate. The increase of film stress could be limited to a lower value even at a high deposition rate. The TFTs fabricated with VHF PECVD a-Si:H and a-SiN_x:H films showed applicable field effect mobility. It is concluded that VHF plasma is useful for high rate deposition of a-Si:H and a-SiN_x:H films for TFT LCD application.     

Bias sensitive multispectral structures for imaging applications

In this paper we present results on the optimization of an pinpii‘n’ type a-Si:H based three color detector with voltage controlled spectral sensitivity. The sensor element was fabricated on a glass covered with Indium Tin Oxide (ITO) and consists of a p-i-n a-SiC:H multilayer structure which faces the incident illumination, followed by a-SiC:H(-p)/a-SiC:H(-i)/a-Si:H(-i′)/a-SiC:H(-n′)/ITO heterostructure, that allows the optically addressed readout.Results show that this approach leads to regionally different collection parameters resulting in multispectral photodiodes. In the polychromatic operation mode different sensitivity ranges are programmed by switching between different biases so that the basic colors can be resolved with a single device. Positive bias is needed under blue irradiation and moderated reverse bias under green. The threshold voltage between green and red sensitivity depends on the thickness of the bottom a-SiC:H (-i) layer, and corresponds to the complete confinement of the absorbed green photons across the pinpi sequence. As the thickness of the a-Si:H i'-layer increases, the self-reverse effect due to the front absorption will be balanced by the decrease of the self-forward effect due to the back absorption shifting the threshold voltage to lower reverse bias.The various design parameters are discussed and supported by a 2D numerical simulation.     

XPS study of the a-C:H/Ti and a-C:H/a-Si interfaces

In this study ultrathin hydrogenated amorphous carbon (a-C:H) films have been grown onto the titanium and amorphous silicon (a-Si) overlayers by direct ion beam deposition using acetylene gas as a hydrocarbon source. X-ray photoelectron spectroscopy (XPS) was used for study of the DLC-Ti and DLC-Si interfaces. It was revealed that a-Si is a good interlayer for improvement of adhesion in the case of diamond-like carbon film deposition onto the steel substrate at room temperature. a-C:H film growth without substantial intermixing occurred on the a-Si. On the other hand, adhesion between the Ti interlayer and the diamond like carbon film was very sensitive to the deposition conditions (presence of the pump oil) as well as structure and stress level of the Ti film. It was explained by strong intermixing between the growing carbon film and Ti. Bad adhesion between the growing DLC film and Ti interlayer was observed despite formation of the TiC. At the same time, formation of the TiO_x was not an obstacle for good adhesion. It is shown that composition of the used hydrocarbon gas, structure of the Ti thin film and mechanical stress in it had greater influence on adhesion with a-C:H film than elemental composition of the Ti interlayer surface.     

Revisiting the B-factor variation in a-SiC:H deposited by HWCVD

In order to understand material properties in a better way, it is always desirable to come up with new variables that might be related to the film properties. The B-parameter is such a variable, which relates to the quality of a-SiC:H films both in terms of electronic and optical properties. B (scaling factor) is essentially the slope of the straight-line part of the (E)^1/2–E (Tauc plot). Due to dependence on a large number of parameters and no detailed research, many previous authors have surmised that B has an ambiguous correlation with carbon content. We have made an attempt to establish the relation between the B-parameter as a quality-indicating factor of a-SiC:H films in both carbon- and silicon-rich material. For this we studied a-SiC:H films deposited by the HWCVD method with broad deposition parameters of substrate temperature (T_s), filament temperature (T_F) and C₂H₂ fraction. Our results indicate that the B-parameter varies considerably with process conditions such as T_F, total gas pressure and carbon content. An attempt is made to correlate the B-parameter with an opto-electronic parameter, such as the mobility edge, which has relevance to the device-quality aspects of a-SiC:H films prepared by HWCVD.     

Microcrystalline silicon growth on a-Si:H: effects of hydrogen

Spectroscopic ellipsometry and secondary ion mass spectrometry have been performed on structures consisting of a microcrystalline silicon film deposited on different a-Si:H substrates. The substitution of hydrogen by deuterium in the microcrystalline growth allowed us to quantify the long-range effects of hydrogen and to distinguish between the different layers. The thicknesses deduced from ellipsometry measurements were in excellent agreement with the secondary ion mass spectrometry profiles. Moreover, we clearly show that the a-Si:H film on which the microcrystalline silicon is deposited can be modified because of the diffusion of hydrogen necessary to the formation of the microcrystalline silicon. However, this modification strongly depends on the deposition conditions and abrupt interfaces can be achieved in some cases.     

Simulated body fluid (SBF) adsorption onto a-SiC:H thin films deposited by hot wire chemical vapor deposition (HWCVD)

Hydrogen amorphous silicon carbon (a-SiC:H) film deposited by the Hot Wire Chemical Vapor Deposition (HWCVD) technique on silicon substrates were soaked in simulated body fluid (SBF). Characterization of the film with different soaking durations in SBF was carried out by Fourier Transform Infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. It was found that the relative amounts of carbon in the a-SiC:H film surface decreases with increase in soaking period. XPS results showed the adsorption of Ca and Mg on the a-SiC:H surface. This indicates the formation of negatively charged surface possibly due to formation of silanol groups or dissolution of carbon to SBF confirming the bioactivity of the material. Contact angle decreased from 74° to 65° during 30 days of soaking in the body fluid. Present study is an attempt to observe the interaction of a-SiC:H film prepared by HWCVD technique with the body environment for its future suitability as artificial heart valve and stent coating materials.